The odor generated by the presence of sulphur compounds in effluent gases has been a problem for a long time. Many different methods, all based on chemical and physicochemical properties derived from sulphur, have been used to solve this problem. Usually, some type of absorption system has been used, based on activated carbon that has been treated with some alkaline or other material that in some way increases the absorption of the polluting agent. Moreover, the chemical oxidation systems involved in the cleansing of gas streams which contain one or more malodorous compounds, have been another possible solution to this problem. Therefore, oxidizing agents have been used, such as sodium hydroxide, sodium hypochlorite and some others on a smaller scale, to cleanse odoriferous streams.
More recently, Meuly, U.S. Pat. No. 4,009,251 in 1977, Hardison, U.S. Pat. No. 4,482,524 in 1984 and McManus, U.S. Pat. No. 4,622,212 in 1986 have used chelated iron to solve the problem of odor generated by H.sub.2 S, in which the oxygen in the gas stream is used as an oxidizing agent in a catalytic system that self-regenerates and leaves elemental sulphur as a final product.
Various attempts have also been made to solve the problem of the polluted emissions from viscose plants, which contain H.sub.2 S and CS.sub.2 in humid air. H.sub.2 S can be absorbed in activated carbon impregnated with potassium iodide, while CS.sub.2 can be absorbed by fine porous, activated carbon. The H.sub.2 S0.sub.4 that is formed is washed away with water and the CS.sub.2 is dissipated with water vapor. Another option is to use activated carbon with a low heavy metal content in order to oxidize the H.sub.2 S, and the resulting H.sub.2 S0.sub.4 is neutralized with NH.sub.3. Nevertheless, it must be noted that these methods are not very appealing for treating large quantities of polluted air that contain relatively low concentrations of the pollutants due to their low efficiency and operating costs. Another alternative for eliminating part of the carbon disulphide from effluent gases, consists of freezing them to a temperature of -0.degree. C., in order to condense part of the carbon disulphide. Once the carbon disulphide is partially removed, the gas is sent to a burner.
Although the technologies that use activated carbon solved the problem of removing a large quantity of pollutants efficiently, the carbon regeneration process is not economical. Besides, the regenerated material does not have the same efficiency as the original material. Moreover, there was still the problem of disposing of the spent carbon. On the other hand, when you cleanse polluted air streams with oxidizing agents or when you use catalytic systems with chelated iron, the operating costs are always significant, mainly due to the consumption of chemical products. If you decide to burn the sulphur compounds, you then have the problem of disposing of the sulphur dioxide.
One or more of the aforementioned methods can be used to solve the problem of odors caused by sulphur compounds, however the operating cost is not very appealing, and in many cases, as has already been demonstrated, the solution to the problem is not definitive, since they generate other types of controversial waste.
A more interesting alternative in recent years has been under development, using biological systems to control emissions into the atmosphere and to treat process gas. These systems have the advantage of offering a final solution for many air pollution problems, as well as also eliminating all sulphur compounds in one single step. They promote biochemical oxidation from sulphur compounds to nonvolatile products by using the life cycles of some sulphoxidizing bacteria, thus resulting in much more economical processes.
For example, Berzaczy et al., in U.S. Pat. No. 4,968,622 in 1990, described a biological process for the elimination of sulphur compounds from a gas stream, obtaining sulphate liquor as a final product. Likewise, in French patent No. 2,331,367, applied for 1976 and assigned to Courtaulds, Ltd., reference is made to certain laboratory studies and a mini-pilot program for a biotechnological process for the elimination of H.sub.2 S from a gas stream, and obtaining a mixture of sulphur and sulphate as a final product.
In our process, you do not have the inconvenience, presented in the previously reported studies, of turning the pollution into another problem, that is turning the sulphur compounds in gas streams into sulphate liquor in another phase. The biotechnological process reported in this paper, eliminates sulphur compounds from a gas stream, and basically transforms them into inoculated sulphur, which has proven to be a valuable product such as an soil enhancer. Another advantage of this invention is that it very efficiently eliminates sulphur compounds.